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A high-capacity sulfur oxide absorbent, cryptomelane, has been described previously. Its SO 2 capacity can be as high as 70 wt %, which is more than 10 times as high as the capacities of standard metal oxide-based SO 2 absorbents. In this study, the stability of cryptomelane under oxidizing, inert, reducing, and lean-rich cycling conditions was determined. Cryptomelane is stable in oxidizing and inert atmospheres. However, it is unstable under reducing atmospheres, converting to lower valent manganese oxide compounds. These low-valent oxides have very low capacity toward SO 2 . Upon reexposing the reduced cryptomelane products to an oxidizing atmosphere, cryptomelane may re-form. Cryptomelane exposed to the types of lean-rich cycles that have been proposed for NO x traps for diesel emission control, over the temperature range 250-550 °C, remains stable and maintains its very high SO 2 capacity. It appears possible to use cryptomelane to protect the NO x traps from sulfur oxide degradation during cyclic leanrich operation.

This study on the immobilization of high-sodium-bearing HLW in synroc indicates that (Na,,,,Nd,,,~)TiO,-type perovskite can be used to incorporate a high content of sodium in synroc. Synroc samples containing 13.0 wt% waste oxide and 5.7 wt% Na,O show very well chemical durability and physical properties. The standard Synroc-C formulation can incorporate only 2 wt7c Na,O, so this study greatly improved the immobilization ability of sodium in Synrocrelated material.